Composite rocket-ram jet fuel



March l, 1960 H. M. Fox

COMPOSITE ROCKET-RAM JET FUEL Filed May 23, 1955 VVVVV INVENTOR.

H.M. FOX BY Mw y yam? ATTORNEYSI COMPOSITE ROCKET-RAM Homer M. Fox,Bartlesville, Okla., 'a'ssignor to Phiiiip's Petroleum Company, acorporation of Delaware Application May 23, 1955, ASerial No. 510,494

9 Claims. (Cl. lill-98) This invention relates to a ducted rocketramjetengine which utilizes 'solid fuels in both the rocket and the fram jetportions -of the engine. In one aspect theinvention f relates to amethod for 'boosting the performance of a ram jet engine with a solidpropellent-rocket and co`i1- comitantly utilizing the rocket Vforsupplying tlre fsolid fuel -to the ram jet portion of the engine.Inanoth'er aspect the invention relates -to a novel combination Esolidrocket -propellant and solid ram jet fuel.

A solid propellent rocket motor commonlycom'prises a combustion chamber,having an exhaust nozzle, tanda solid combustible charge placedwithin`the combustion chamber. volume of gases under pressure which isdischarged through the nozzle at high velocity. The reaction result-ingfrom Athe flow of gas through the nozzle Ycreates the propulsive thrust.A rocket motor does Inot 'require Combustion of the charge produces -adarge air for combustion of the fuel and such motor produces thrust atall speeds, including take-olf.

-A ram jet or an athodyd engine comp 'ses a ductin'tfc which air entersunder pressure as a result of forward motion of the engine and adischarge nozzle from 'which propulsive gases are expelled. Fuel ismixed with-the air in the -duct and ignited andthe combustion productsare discharged from the rear end of the duct at-high velocity so as toprovide the forward populsive thrust. VThis type of engine produces noappreciable thrust vuntil high air speeds are attained so as to providesucient air for` the satisfactory combustion of the fuel. K

In order to provide a ljet propulsion device which attains high thrustover a large range of operating conditions and which exhibits low valuesYof fue'1`consumption at highspeeds, a combination powerplant comprisinga ram jet propulsion device and a rocket propulsion device has beendeveloped. vIn one form of Asuch a combination engine, vcalled a ductedrocket-,ram jet engine, a rocket motor is mounted insi'dfethe ram Yjetcasing`in front ot the Vram jet combustion chamber Vand'air isintroduced into the combustion chamber vby ejector action created by thedischarge oftherpropellent decomposition products into the exhaustsystemof the ram `jjet engine. The induction of air into the rairijetcombustion chamber by the rocket motor 'permits the ram jetffuel, whichAis injected into the ram jet 'combustion'chambe in a zone downstreamfrom the rocket motor, to Ibe burned and thrust to be developed at zerovflight speed. In these power plants of the prior art, the ram jetfuelisaliquid and this necessitates the incorporation of a 'complex fuelmetering system and a vplurality of fuel reservoirs.

Power plants intendedfor high speeds, includirigsuper-l sonic speeds,require considerations of fuel "and/ or weight specific impulse, fueland/ or propellent 'densityiimpulfse, and air specific impulse. vInorder to 'arrive at optimum performance properties for 'such highspeedpower plants, particularly air breathing aircraft and Vmorelparticularly missiles, acompromise Voften ihasta be fdra'wn. "There11is a considerable number of solid 4materials available as fuels whichpossess Eagood .combination of ithese rp'ropev tiesfasipower'pla-ntfuels. Metals such 'as beryllium, boron, magnesium-and aluminum, 'aswell as some non-'metalsincluding".V carbon, display :desirable"properties lof vfuel weightiispecic limpulse and :f uelfd'e'nsit'y"impulse as Well as providing `excellent air `speciticirnpulse in amotor wherein they are utilized. These solid. fuels, however, presentianumber of practicalproblems which have been almost insurmountable.Hydrocarbon slurries. 'of` such fuels are diflcult to stabilizewithoutpelabo'rate mechanical equipment in the'fuel tank. If the 'slurrycan bestabilized, it is then dihicult to 'pump and `to inject properlyVsuchf'slurry into the combustioncham'ber. Anotherfmethod has 4vbeenproposed for utilizing powdered solid fuels which involves adding thematerials to solid propellants. Problems encountered in such proposedmethodV include the high loading `of solids in an Iorganic matrix landthe explosive Isensitivity -of'such a mixture. w

'It -is an object of -this invention -to provide a'practical Y Ameans'of utilizingv powdered solid fuel as ythe'source of Other and furtherobjects and advantages Vof `this'invention will fbe apparent tooneskilled i'n the art "upon study of the disclosure of the `inventionincluding the `appended kdrawing wherein:

Figure 1 ,is aschematic fsectional yview of --a' ducted rocket-'ramjet'motor constructed inaccordance -withanv embodiment ofthe invention,and

:Figure 2 is a'sectionaflvscheniatic view iofamodification l of Athevducted rocketera'm `jet motor 'of `this invention.`

The present `invention ,provides `a :ducted rocket-ram jet power plantin` which sa :rocket lphase .exhaust lgas Vrich rin powdered fuel Ais-ibfurned with airinlthe ramjet'phasevof the power plant. The ductedrocket-'ram jet power plant of .this tinvention idevelops -thrust atzero l:air speed Vand at low speeds where ordinary ram jet operationisineicient yif not impossible. The power plant of this inven' i tionalso develops high thrustand high cmbustionfefill ciency over Aa widerange of operatingv conditions `of the ram jet combustion process;y Theconstruction of the power plant of this-invention is'alsoY -relativelysimple in comparison to other .ductedrrocket-ram ljet power plants in.that fa :solid propellant -is used, therefore, the need for .a Jcomplex.fuel metering 4Systemand fa plurality .of

fuel reservoirs is eliminated.

.'In the presentdnventiou, afconventional type solid propellantandapowdered fuel, `oria mixture of powdered fuels, and'fan organicrbinderfare `preferably arranged :in the rocket `rriotor'section of thefpower :plant as alternate disks. The conventional :typefsolidfpropellant is decomposed in the rocket -motor and as the'gases whichresult from decomposition -of thersolid :propellant yare expelledfrom-the lrocket motor, the powdered: fuel is carried along e andintroduced into `,the'combu'stion l,chamber of the ram jet and thereburned :in airto ,provide propulsive force for the ipower plant.'Ihescblid` propellant .utilized should have at least a :moderatelyehigh:reaction temperature, and should .ordinarily have aslong burning time,`.although propellants :having fast burning ratesfcan also be uscdeffectively. xA particularly suitable and Iparticularly ,preferredpropellant 4comprises ammonium nitrate as the oxidant :and ia'solidpolymeric vorganiccompoundgsuch I as a copolymer :of butadiene 4andmethylvinylpyridine @por a -lcopolymer of butadiene Aand istfyrene, tasthe .hinder and-fuelfthereo iagentsfsuchtlas quaternizing or l2,926,613. Ptented Mar. l

:1. vulcanizng agents are incorporated in the copolymer. Suitableburning rate catalysts which can be used include rouge, ammoniumdichromate, Prussian blue, Milori blue, and the like. The compositionand method of preparation of a propellant of this type is Adescribedand-clair ne d in copending application Serial No. 284,447,.filedA`pril25, 1952, by W. B. Reynolds and I. E. PritchardlgAnother suitablepropellant comprises ammonium perchlorate and polysulde rubber. Any ofthe known solid monopropellants and composite propellants can. be used.

The ram jet fuel used in this invention is the powdered fuel carried inthe rocket exhaust gas to the combustion chamber of the ram jet portionofthe power plant. The powdered fuel can be any high energy solid suchas carbon, alkali metals, beryllium, boron, magnesium, aluminum, and thelike, or any combination of two or more of these fuels. v

The binder for the solid fuel can be asphalt, cellulose, rubber,including natural rubber and synthetic rubbers such asbutadiene-methylvinyl-pyridine copolymer or butadiene-styrene copolymer,or other suitable organic binder materials. If desired, a high energynitro-polymer, which could provide additional energy. for the system,can also be used as the binder.

The amount of binder incorporated with thepowdered fuel will ordinarilybe the minimum amount required to maintain the powdered fuel in acoherent mass. having the required structural strength to withstandstorage and handling. The requirements for strength, however, are nothigh because the powdered fuel component will vbe supported by therocket fuel component of the charge. It is desirable that the powderedsolid fuel component be of such character that it will decompose anderode easily when subjected to the hot gases evolvedfrom the burningrocket fuel. The utilization of ordinary techniques for theincorporation of fairly viscous polymeric compounds containing as littleas weight percent of binder, will produce a satisfactory solid product.A special technique will produce solid grains of powdered fuelcontaining as little as 1 weight percent of binder. This specialtechnique comprises intimately admixing the powdered fuel with an excessof a uid binder material such as lacquer or shellac and centrifuging themixture to remove excess fluid. After molding or extruding and curing adense charge of high structural strength is obtained.

The fuel which is utilized in the present invention can be processed ina number of ways. For example, the fuel charge can.be pressure molded,extruded, or cast into disks of desired size and shape. Disks ofpropellant can be similarly processed and these disks of fuel andpropellant can then be assembled alternately and pressed together withinthe rocket motor casing. Thus assembled, the powdered fuel Vdisks wouldact as restrictors for the propellant charge. If a copolymer, such asbutadienemethylvinylpyridine copolymer, is utilized as the binder forboth the solid propellant and the powdered fuel charge, these units canbe assembled and pressed together and cured as a unit. The disks ofsolid propellant and solid fuel can be either case-bonded or not asdesired. The composite charge of alternate disks of solid propellant andsolid fuel can conform to any desired configuration such as aninternal-external burning charge or an internal burning charge having acenter opening in the form of a star or other configuration dependingupon the desired amount of area exposed to burning. The solid propellantand powdered fuel charges can be two concentric charges, however, thepreferred arrangement involves the use of alternate disks arranged so asto form a charge of internal burning configuration. The disks can be ofequal thickness or the thickness of the disks can be varied so thatmore'or less fuel is supplied to the ram jet engine, as desired.

One particular modification of the invention utilizes a firstv thickdisk of-a Vfast -hurning` propellant-forinitial starting of the powerplant followed by successive thinner disks of slow burningppropellant,alternated with increasingly thicker disks ofr powdered fuel.

As an example of a preferred form of the improved rocket-ram jet engineof this invention, reference is now made to Figure 1 wherein there isshown a streamlined, elongated, cylindrical ram jet casing 10, having aforward end 11 through which inlet air is introduced, a centrallylocated combustion chamber 12 and an exhaust nozzle 13 at the rear ordownstream end of. casing 10. A stream lined, elongated, cylindricalrocket motor 14 having a pointed forward end 15, a venturi dischargenozzle 16 at its lopposite end, and containing al charge comprising asolid propellant 17 and a composite mixture of powdered fuel and organicbinder 18 arranged in alternate disks is positioned in ram jet casing10. An electric squib 19, which comprises a charge of powder ignited byelectrical means, is mounted within yrocket motor 14 so as to provide ameans for igniting the solid propellant 17. The outside, diameter of;rocket motor 14 is smallerthan the inside diameter of casing 10, and,therefore, an annular space 20 is formed between the front end of casing10 and motor 14 so as to supply air to the enlarged combustion zone` 12downstream from rocket motor 14. Rocket motor 14 is rigidly mountedwithin casing 10 by means of spokes21 and 22. Flame holder 23 ispositioned in the ram` jet combustion chamber 12 so as to aid in theignition and burning of the ram jet fuel in air by providing turbulenceandmixing. f

In the operation ofthe ducted rocket-ram jet engine of this invention,the solidpropellant is ignited by electric squib 19. The rocketpropellant decomposition products erode and carry with them the powderedfuel `present in disks 18 and are discharged rearwardly intorthe Vrarnjet combustion chamber 12. The powdered ram jet fuel is burned inchamber 12 in the air introduced through the inlet air diffuser sectioncomprising annular space 20 and thrust is developed by exhaustion of thecombustion products of the rocket propellant and the ram jet fuel andheated air through the ram jet exhaust nozzle 19.

As a further example of the rocket-ramv jet engine of this invention,reference is now made to Figure 2 wherein there is illustrated amodification of my invention. Like numerals refer to like memberswhenever possible in Figures 1 and 2. Air enters the rocket-rain jetthrough the axial opening 24. A plurality of rocketchambers 25 arespaced around the periphery of vcasing 10. vThe rocket chambers 25 arevsubstantially filled with alternate disks of solid propellant v17 andpowdered fuel-organic binder disks 18. Asthe propellant burns in each ofthe rocket motors the powdered fuel is carried with the products ofcombustion from each of the rocket motors and is burned with air in theram jet combustion chamber 12. Propulsion is developed by the exhaustionof the combustion products of the rocket propellant and the ram jet fueland air through ram jet exhaust nozzle 13. The burning time of therocket fuel and powdered jet fuel can be lengthened by successiveburning of the charges instead of simultaneous burning of the charges.As an example of successive burning, opposite ,p eripheral charges canbe burned simultaneously until all ofthe charges have been burned.

The power plant of the present invention presents many advantages overthe prior art methods of operating rocket-ram jets. By utilizing a solidrocket propellant and a composite mixture of powderedsolid fuel andorganic binder as the ram jet fuel, in accordance with the presentinvention, the complex fuel metering systems and fuel tank arrangementsrequired for liquid fuel systems of the prior art rocket-ram jets, areeliminated. The construction is greatly simplified thereby rendering thepower plant more rugged and more. reliable in operation. lnaddition, therocket-,ram jet provides Statie thrust and is self-starting. The ductedrocket-ram jet engine of this invention provides an increase in theeciency of the utilization of air and affords efficient operation atexceedingly high altitudes.

The invention has been described with particular reference to missiles,however, the ducted rocket-ram jet engine of this invention can also beutilized in starting a piloted ram jet powered aircraft. In suchapplication one or more of the ducted rocket-ram jet engines are mountedupon the aircraft in a manner similar to JATO installations. Theseengines are then employed to take the aircraft off the ground and up tothe operating speed of the main ram jet engine of the aircraft. Afterthe ducted rocket-ram jet engines have served their purpose, they can bedropped and replaced at the end of the llight, or left in place andrecharged at the end of the flight.

EXAMPLE Performance advantages of the ducted rocket-ram jet engine ofthis invention are illustrated in the following tabulation. ln thisexample powdered boron was selected as the ram jet fuel and methylnaphthalene was used as the boron binder for convenience in thecalculations. The composition of fuel B was chosen to give the samevolume of rocket propellant and ram jet fuel.

Table l Total Volume Total Pro- Oxidizer Re- Air Re- Fuel Impulserellant in Proquired quired (lo-sec.) Repellant for Pro (lbs.)

quired (lb.) pellant (lb.) (111.3)

Methyl N aphthal 2, 200 l. 0. 00 28. 3` 13.1 2, 200 0. 85 0. 00 35. 712. 9 2, 200 2. 0. 82 31. 0 10. 2 2,200 1.84 0.63 27. 2 10. 4 2, 2001.47 0.30 21. 0 10.8

Composition of the rocket propellant and ram jet fuels are:

Weight percent 80 Wt. percent ammonium perchlorate and 2O Wt. Methylpercent Naphth- Boron butadiene/ alene methylvlnylpyridine binder Disc17 Disc 18 Variations and modifications are possible within the scope ofthe disclosure of the present invention, the essence of which is a novelsolid fuel ducted rocket-ram jet power plant and a method for preparingthe novel solid composite fuel.

That which is claimed is:

1. The method of producing a composite rocket-ram jet solid fuel chargewhich comprises incorporating 50 6 to parts by weight of ammoniumnitrate, 10 to 50 parts by weight of a copolymer of butadiene and amaterialcopolymerizable therewith selected from the group consisting ofmethylvinylpyridine and styrene, 1 to V10 parts `by weight of a burningrate catalyst, and curing agents; forming said material into disks;intimately ad i mixing at least one powdered fuel selected from `thegroup consisting of carbon, alkali metals, beryllium, boron, magnesium,and aluminum with a binding amount of an organic binder selected fromthe group consisting of butadiene-rnethylvinylpyridine copolymer andbutadienestyrene copolymer, and curing agents; formingesaid materialinto disks; assembling alternate disks of ammonium nitrate containingmaterial and solid fuel containing ma# terial to form a composite fuelcharge; and compressing and curing said charge.

2. A composite rocket-ram jet'fuel consisting essen-V tially of aninternal burning charge ofalternate disks of (l) a solid rocketpropellant comprising about 50 to 90 parts by weight of anoxidizingagent selected from the.

group consisting of ammonium nitrate and ammonium perchlorate, l0 to 50parts by weight of a copolymer of Y butadiene and a material selectedfrom the group consisting of styrene and methylvinylpyridine, and v'l to10 parts by weight of a burning rate catalyst; and (2) 'a solid ram jetfuel comprising about 10 parts by weightkmethyl naphthalene and about 90parts by weightof a powdered fuel selected from the groupcoinsisting ofcarbon, alkali metals, beryllium, boron, magnesium, and aluminum.

3. The fuel of claim 2 wherein Vthe powdered fuelis an alkali metal. Y Y

4.` The fuel of claim 2 wherein the powdered fuel is carbon.

5. The fuel of claim 2 wherein the powdered fuel is beryllium.

6. The fuel of claim 2 wherein the powdered fuel boron. v

7. The fuel of claim 2 wherein the powdered fuel is magnesium.

8. Thel fuel of claim 2 wherein the powdered fuel is aluminum.

9. A composite rocket-ram jet fuel in cylindrical grain consistingessentially of alternate disks of (l) a solid rocket propellantcomprising about 50 to about 90 parts by weight of a solid inorganicoxidizing salt and about 10 to about 50 parts by weight of a solidpolymeric organic binder; and (2) a solid ram jetfuel comprising apowdered fuel selected from the group con sisting'of carbon, alkalimetals, beryllium, boron, magnesiurn, and aluminum incorporatedpin anorganicrbinder.

References Cited in the le of this patent A UNITED STATES PATENTS2,408,252

the form of a

2. A COMPOSITE ROCKET-RAM JET FUEL CONSISTING ESSENTIALLY OF A INTERNALBURNING CHARGE OF ALTERNATE DISKS OF (1) A SOLID ROCKET PROPELLANTCOMPRISING ABOUT 50 TO 90